Low-contaminant resols for cements

ABSTRACT

Resols which are suitable for use as binders for cements, laminates, impregnations and abrasives having low after-shrinkage have a free phenol content of less than 5% by weight and are in the form of mixed condensates of trifunctional phenols with respect to formaldehyde and alkylidenepolyphenols in a molar ratio of phenolic hydroxyl groups in the trifunctional phenols to hydroxyl groups in the alkylidenepolyphenols of 9:1 to 3:7 with formaldehyde in a molar ratio of the sum of phenolic hydroxyl groups to formaldehyde of 1:1.2 to 1:2.0.

The invention relates to low-contaminant resols which, while having goodsolvent resistance and a low phenol content, can be used in cementshaving low after-shrinkage, to the preparation of such resols and totheir use for cements, laminates, impregnations and abrasives.

U.S. Pat. No. 4,596,840 discloses resols for cements having lowafter-shrinkage. However, cement solutions prepared from these resolshave a phenol content between 7 and 10% by weight.

The free phenol content in the known resol-containing resin solutionsprovides valuable application properties. In cements, it affects inparticular after-shrinkage. On the other hand, the phenol content ofpreparations is regulated by law. Preparations having a phenol contentabove 5% by weight must be labeled as "toxic", that is, they must betreated as industrial toxic substances. For reasons of occupationalhygiene, it is therefore important to limit the maximum phenol contentin this preparation to values below the toxicity limit of 5% by weight.

As is known, the free phenol content in a resol depends very greatly onthe level of formaldehyde (relative to the phenol portion), duringpreparation. Accordingly, one way of obtaining resols having a phenolcontent below 5% by weight is to increase the level of formaldehyde.However, if these resols are synthesized using different levels offormaldehyde, resulting in different free phenol contents, the cementsprepared therefrom are found to have sufficiently low after-shrinkagevalues only if the phenol content is clearly above 5% by weight(comparative experiments 2.1-2.4). U.S. Pat. No. 3,979,218 describes aprocess for preparing low-contaminant resols for cement solutions. Tothis end, phenols, alkylated phenols and formaldehyde are reacted andthe phenolic hydroxyl groups thereof are then partially etherified.Cement solutions prepared from such resols have a low phenol content of,in some cases, even less than 1% by weight. However, owing to the alkylether groups incorporated, the cured products are naturally susceptibleto organic solvents such as toluene and butene acetate and accordinglydo not reach the resistance to chemicals of the non-etherified products.

The object of the present invention was therefore to providesolvent-resistant resols which have a free phenol content of less than5% by weight and are suitable for preparing cements having a lowafter-shrinkage.

According to the invention, the object is achieved by resols obtained bymixed condensation of formaldehyde, trifunctional phenols with respectto formaldehyde and alkylidenepolyphenols in a molar ratio of phenolichydroxyl groups in the trifunctional phenols to phenolic hydroxyl groupsin the alkylidenepolyphenols of 9:1 to 3:7 and a molar ratio of the sumof phenolic hydroxyl groups to formaldehyde of 1:1.2 to 1:2.

Accordingly, the invention relates to resols which are suitable for useas binders for cements, laminates, impregnations and abrasives havinglow after-shrinkage and have a free phenol content of less than 5% byweight, preferably less than 4% by weight, in particular less than 3% byweight, and are in the form of mixed condensates of trifunctionalphenols with respect to formaldehyde alkylidenepolyphenols in a molarratio of phenolic hydroxyl groups in the trifunctional phenols tohydroxyl groups in the alkylidenepolyphenols of 9:1 to 3:7, preferably7:1 to 3:5, in particular 5:1 to 2:3, with formaldehyde in a molar ratioof the sum of phenolic hydroxyl groups to formaldehyde of 1:1.2 to1:2.0, preferably 1:1 to 1:1.8.

As used therein, trifunctional phenols with respect to formaldehyde arephenols in which both o positions and the p position relative to thephenolic hydroxyl group are unsubstituted and reactive.

The most suitable trifunctional phenol with respect to formaldehyde isphenol itself. However, it is also possible to use alkylphenols, forexample m-cresol, m-ethylphenol. The trifunctional phenols can be usedindividually or else in a mixture.

In addition to these trifunctional phenols, small amounts, preferably upto 10 mol %, in particular up to 5 mol %, relative to the amount oftrifunctional phenols, of other substituted bi- or mono-functionalphenols with respect to formaldehyde, for example o-, p-cresol, can alsobe used.

Alkylidenepolyphenols are compounds in which at least two phenolradicals bridged by an alkylidene radical are present. Examples ofcompounds which serve as alkylidenepolyphenols are novolaks obtainedfrom phenol and oxo compounds. The number-average molecular weight ofthese novolaks is preferably between 200 and 1000, in particular between400 and 750. Apart from the phenol used for preparing the novolaks,small amounts of substituted phenols can also be present. Examples ofsuitable oxo compounds for preparing novolaks are acetaldehyde,propionaldehyde, butyraldehyde, iso-butyraldehyde or higher aldehydeshaving up to 10 carbon atoms, but preferably formaldehyde. Mixtures ofnovolak obtained from different oxo compounds can also be used.

Useful alkylidenepolyphenols are also bisphenols linked by methylene,ethylidene, propylidene, iso-propylidene, butylidene or iso-butylidenebridges or mixtures thereof.

These alkylidenebisphenols can also carry alkyl substituents preferablyhaving 1 to 4 carbon atoms. Particular preference is given to the use of2,2-diphenylolpropane, which is a bisphenol linked by an iso-propylidenebridge.

In order to bind excess formaldehyde, the resols according to theinvention can contain formaldehyde scavengers in amounts of up to 10% byweight, preferably of up to 5% by weight. Compounds which are suitablefor this purpose are basically any substances which react spontaneouslywith formaldehyde, for example dicyandiamide, melamine, urea,ethyleneurea and other cyclic urea derivatives, guanidine,benzoguanamines and other compounds which form aminoplastic resins.

The present invention also provides a process for preparing the resolsaccording to the invention. Preparation of the resols takes place inhomogeneous phase under the conditions customary in phenolic resintechnology at temperatures between 20° and 100° C., preferably 40° and80° C.

Preferably, basic catalysts, for example amines, alkaline earth metaloxides, alkaline earth metal hydroxides or alkali metal hydroxides, inparticular sodium hydroxide, are added to the reaction mixture. Afterthe reaction is complete, the catalysts are preferably neutralized byaddition of acid.

The time of addition of the alkylidenepolyphenol is essential to theprocess according to the invention. Premature addition leads to resinshaving a very high phenol content (Comparative Example 3). On the otherhand, addition of the alkylidenepolyphenol must not take place too latesince otherwise the viscosity, the water compatibility and otherimportant application properties will be adversely affected. Thereforeit is necessary to closely monitor the course of the reaction bymeasuring the viscosity and the formaldehyde content. An optimum mode ofoperation is first to charge the reaction vessel with the trifunctionalphenols and, if desired, the mono- and bifunctional phenols togetherwith the total amount of formaldehyde and the catalyst and to allow thereaction to proceed until 50 to 90%, preferably 60 to 90%, of theformaldehyde used has been reacted. The alkylidenepolyphenols are thenadded, and the reaction is continued until reaching the desired endpoint, which is usually determined by measuring the viscosity.

In order to reduce the formaldehyde content in the resol, a formaldehydescavenger can be added after the reaction is complete.

The invention also relates to the use of the resols according to theinvention as binders for cement resins, laminating resins andimpregnating resins for porous molded articles or else as binders forsheet-like abrasives.

Especially when cements are prepared, suitable fillers, preferablygraphite powder, coke powder, are usually added to the resols. With theresols according to the invention, other additives which otherwise arecustomary in cements, such as epoxy compounds, chloroalkanes and furanederivatives can be omitted. However, if required, the additivesmentioned can also be used. In addition, organic solvents can also beadded to the resols according to the invention. Of these, those whichare not toxic, for example acetone, are preferred.

When the resols according to the invention are employed forimpregnations and abrasives, curing of the resols preferably takes placeby heating. In order to achieve good curing of the resols in cements andlaminates, in particular when used at low temperatures, it is usuallynecessary to add strong inorganic or organic acids, such as sulfonicacids, as catalysts. Advantageously, sulfonyl chlorides can also be usedor included as latent acids. A detailed description of the preparationof cements and methods for testing them are described in thepublications EP-A 0,158,871 and U.S. Pat. No. 3,977,218 mentioned at thebeginning.

The cements obtained from resol resins according to the inventionpossess all necessary properties of conventional cements and, inaddition thereto, have, in accordance with the invention, the advantageof a low phenol content and furthermore good resistance to chemicals.

The invention is described in more detail by the examples which follow.Parts and percentages are by weight unless stated otherwise.

EXAMPLE 1

The glass reaction vessel is equipped with stirrer, thermometer, heatingand cooling.

282 parts of phenol are melted, and 30.3 parts of 33% sodium hydroxidesolution are added, and the resulting mixture is heated to 60° C. Thisis followed by first adding 121.5 parts of an aqueous 37% formaldehydesolution and 173.3 parts of 91% paraformaldehyde over a period of onehour and stirring the mixture at 60° C. until, two hours after additionof the formaldehyde is complete, the formaldehyde content reached in thereaction batch is 7.12%, which corresponds to a formaldehyde consumptionof 72%. At this point, the reaction solution has a viscosity of 137mPa.s (23° C.), an evaporation residue (1 h/135°C.) of 71% and unlimitedwater compatibility. 228 parts of 2,2-diphenylolpropane are then addedto the batch, and the resulting mixture is stirred until after 150minutes a viscosity of 160 mPa.s (23° C.) is reached. At this point, thereaction mixture contains 1.7% of unreacted formaldehyde, an evaporationresidue of 79.6% (1 h/135° C.) and a water compatibility of 1:1.6 (23°C.) and 3.8% of free phenol. Taking into consideration the samplestaken, the yield corresponds to that of the substance used.

EXAMPLE 2

329 parts of phenol are melted in the apparatus of Example 1, 60.5 partsof 33% sodium hydroxide solution are added followed by addition of 121.5parts of an aqueous 37% formaldehyde solution and 231 parts of 91%paraformaldehyde at 60° C. Three hours after addition of formaldehyde iscomplete, 90% of the formaldehyde used has been consumed at aformaldehyde content of 3.4%. The reaction mixture has a viscosity of344 mPa.s at an evaporation residue of 71.3% (1 h/135° C.) and iswater-miscible in any ratio. 171 parts of 2,2-diphenylolpropane are thenadded, and stirring of the resulting mixture at 60° C. is continueduntil after a reaction time of 80 minutes a viscosity of 1135 mPa.s (23°C.) is reached. At this point, the resin has a formaldehyde content of1.7%, an evaporation residue of 751.1% (1 h/135° C.) and iswater-compatible in a ratio of 1:1.95. The unreacted phenol content is1.7%. The batch is allowed to continue the reaction until after anotherhour at 60° C. a viscosity of 1600 mPa.s (23° C.) is reached. Duringthis period, the free formaldehyde content drops to 1.3%, while thewater compatibility remains virtually unchanged at 1:2. The free phenolcontent is 1.6%. 10 parts of urea are then added per 300 parts of resinand the batch is stirred at 60° C. for another hour and then cooled. Atan unchanged phenol content of 1.6%, the unreacted formaldehyde contentis 0.4%, the viscosity is 1820 mPa.s and the water compatibility is1:2.1.

EXAMPLE 3

In the apparatus according to Example 1, 30.34 parts of phenol, 3.25parts of 33% sodium hydroxide solution, 23.97 parts of aqueous 37%formaldehyde solution and 13.79 parts of 91% paraformaldehyde arereacted at 60° C. until after 3 hours a formaldehyde content of 4.2% isreached. 24.53 parts of 2,2-diphenylolpropane are then added, andcondensation is continued at 60° C. until after 7 hours a viscosity of800 mPa.s (23° C.) is reached. 4.6 parts of urea are then added, thebatch is maintained at 60° C. for another hour, cooled and removed fromthe reaction vessel. The resin has a viscosity of 750 mPa.s (23° C.), anevaporation residue of 70.5% (1 h/135° C.), a phenol content of 2.8%, awater compatibility at 23° C. of 1:0.9 and a formaldehyde content of0.27%.

This resin is tested for use as a cement. To this end, 70 parts of theresin solution are mixed with a curing agent powder, a preparation of 50parts of graphite powders. 44 parts of coke powder and 6 parts ofbenzenesulfonyl chloride. The maximum pot life of the mixture is 75minutes at room temperature. The mixture then cures to give a solidcement material. After 24 hours, the surface hardness (Shore D) is 55units, after 48 hours, it is 65 units. After 8 days of storage at roomtemperature, the modulus of elasticity of the cured cement mass is0.715·10⁻⁴ N·mm⁻².

The aftershrinkage of the cement is measured as follows:

Test specimen: a cylinder having a diameter of 2.5 cm and a length of9.5 cm.

At both ends, measuring marks made of glass are attached. The totallength of the test specimen, including measuring marks: about 10.5 cm.

Preparation of the test specimens: the cement is poured into apolyethylene form, and the cured cement cylinder is removed after 24 h.

Measurement: the first measurement (reference measurement) takes placeimmediately after the test specimen has been removed from the form andthe measuring marks have been attached by means of a micrometer screw.The numbers given are a measure of the linear shrinkage, expressed inpercent, relative to the original length of the test specimens at roomtemperature.

The aftershrinkage of the cured cement is:

    ______________________________________                                        Time       Linear shrinkage                                                   ______________________________________                                         8d        0.1368%                                                            14d        0.1578%                                                            21d        0.1824%                                                            28d        0.2070%                                                            50d        0.2140%                                                            ______________________________________                                    

Test of the Stability of the Cement

The stability test is carried out in accordance with DECHEMA guidelines"Chemische Bestandigkeit von Beschichtungs-, Verlege- und Verfugemassen"(Chemical stability of coating, laying and joint-filling compositions).

Test specimen: a cylinder having a diameter of 2.5 cm and a length of2.5 cm.

Preparation of the test specimens: the cement is poured into apolyethylene form, and the cured cement cylinder is removed after 24 h.

Stability Test:

The stability test is carried out after storing the test specimens atroom temperature for 8 days and soaking them in the relevant test liquidat room temperature. After a period of 1000 h, the test specimens areremoved from the test liquid. They are then rated by the followingcriteria:

weight change in percent, relative to the weight before soaking

visual inspection with respect to surface glass, color, cracking,swelling

surface hardness in Shore D compared with the initial value beforesoaking

compressive strength compared with the initial value before soaking

Rating: for rating the cement as being resistant, the following criteriaare used:

surface unchanged

weight change up to at most 2%

reduction in compressive strength up to at most 10%.

The cements according to the invention are resistant to chloroform, 20%acetic acid, 20% hydrochloric acid, 20% sulfuric acid, toluene anddistilled water. The test specimens have limited resistance to butylacetate and 70% sulfuric acid. The test specimens are not resistant toacetone, bleaching liquor, 15% sodium hydroxide solution and 15% nitricacid. The resistances correspond to those of conventional phenol resincements.

Comparative Experiment 1

Test of a conventional phenolic resin cement for use as cement.

A conventional phenolic resin cement solution, ®Asplit CN (Hoechst AG),having a free phenol content of 8.2%, a free formaldehyde content of0.4% and a viscosity of 830 mPa.s at an evaporation residue of 72% (1h/135° C.) is mixed with the cement powder described in Example 3, andthe mixture is processed in the same manner to give a cement specimen.The aftershrinkage test gives the following values:

    ______________________________________                                        Time       Linear shrinkage                                                   ______________________________________                                         8d        0.1754%                                                            14d        0.1894%                                                            21d        0.2070%                                                            28d        0.2140%                                                            50d        0.2210%                                                            ______________________________________                                    

The chemical resistance test gives the same values as in Example 3.

Comparative Experiments 2.1-2.4

To find out what effect the phenol/formaldehyde molar ratio and theunreacted phenol and formaldehyde content resulting therefrom have onaftershrinkage, conventional resols are prepared and tested for use ascement. The resols are prepared by the following procedure:

940 parts of phenol are melted in the apparatus from Example 1, 60.5parts of 33% sodium hydroxide solution are added, and the mixture isreacted at 70° C. with aqueous formaldehyde and paraformaldehyde until aviscosity of 800 mPa.s (23° C.) is reached. The levels of aqueousformaldehyde, paraformaldehyde, and the properties and characteristicdata obtained are shown in the table below:

    ______________________________________                                        Experiment      2.1      2.2     2.3   2.4                                    ______________________________________                                        Phenol/formaldehyde                                                                           1:2.2    1:2.0   1:1.8 1:1.6                                  molar ratio                                                                   Amount of 37%   270 g    270 g   270 g 270 g                                  formaldehyde                                                                  Amount of 91%   616 g    550 g   486 g 412 g                                  paraformaldehyde                                                              Viscosity [mPa · s (23° C.)]                                                  780      840     800   780                                    Evaporation residue                                                                           72.2%    74.3%   74.4% 73.9%                                  (1 h/135° C.)                                                          H.sub.2 O compatibility (23° C.)                                                       1:1.6    1:1.2   1:0.9 1:0.6                                  Residual CH.sub.2 O content                                                                   4.03%    3.0%    1.45% 1.25%                                  Residual phenol content                                                                       4.6%     5.8%    7.7%  9.75%                                  ______________________________________                                    

The test for use as cement shows that the chemical resistance of thecements is comparable to that listed in Example 3 and ComparativeExperiment 1. The measurement of aftershrinkage gives the followingvalues:

    ______________________________________                                        Linear shrinkage                                                              Time/experiment                                                                          2.1      2.2       2.3     2.4                                     ______________________________________                                         8d       0.1817%   0.1800%   0.1754% 0.1447%                                 14d       0.2278%   0.2103%   0.1894% 0.1052%                                 21d       0.2524%   0.2424%   0.2070% 0.1298%                                 28d       0.3105%   0.2929%   0.2140% 0.1538%                                 50d       0.3807%   0.3456%   0.2210% 0.1859%                                 ______________________________________                                    

Comparative Experiment 3

30.34 parts of phenol and 24.53 parts of 2,2-diphenylolpropane aremelted in the apparatus from Example 1. 3.25 parts of sodium hydroxidesolution are added and the mixture is reacted with 23.97 parts ofaqueous 37% formaldehyde solution and 13.97 parts of 91%paraformaldehyde as in Example 3. After addition of the formaldehyde,the reaction is carried out first at 60° C. for 3 hours until aviscosity of 207 mPa.s is reached. Since the reaction rate at thistemperature is too slow, the condensation is then carried out at 70° C.for 6 hours until a viscosity of 850 mPa.s is reached and is thenstopped. The formaldehyde content is 1.13% and the water compatibilityat 23° C. is 1:1.7%. The free phenol content is 11.3%.

What is claimed is:
 1. A resol for cements, laminates, impregnations andabrasives having low aftershrinkage having a free phenol content of lessthan 5% by weight and being in the form of mixed condensates of at leastone trifunctional phenol with respect to formaldehyde andalkylidenepolyphenols in a molar ratio of phenolic hydroxyl groups inthe trifunctional phenols to hydroxyl groups in thealkylidenepolyphenols of 9:1 to 3:7 with formaldehyde in a molar ratioof the sum of phenolic hydroxyl groups to formaldehyde of 1:1.2 to1:2.0.
 2. A resol as claimed in claim 1, wherein the trifunctionalphenol is phenol.
 3. A resol as claimed in claim 1, wherein thealkylidenepolyphenols are novolaks obtained from phenol andformaldehyde, the number-average molecular weight of which is between200 and
 1000. 4. A resol as claimed in claim 1, wherein thealkylidenepolyphenols are bisphenols containing methylene, ethylidene,propylidene, iso-propylidene, butylidene or iso-butylidene bridges.
 5. Aresol as claimed in claim 1, wherein the resol contains formaldehydescavengers.
 6. A process for preparing a resol as claimed in claim 1 inthe presence of a basic catalyst in a temperature range from 20° to 100°C., which comprises using the total amount of trifunctional phenols andof formaldehyde in a first step and continuing the reaction until aformaldehyde consumption of 50 to 90% of the formaldehyde used isreached and then adding the alkylidenepolyphenols and continuing themixed condensation.
 7. The process as claimed in claim 6, wherein aformaldehyde scavenger is added at the end of the mixed condensation. 8.The process as claimed in claim 6, wherein the catalyst is neutralizedor partially neutralized after the reaction is complete.
 9. A cementresin containing a resol of claim
 1. 10. A laminating resin containing aresol of claim
 1. 11. An impregnating resin for porous molded articlescontaining a resol of claim
 1. 12. A binder for sheet-like abrasivescontaining a resol of claim 1.